Suppressive effect of dexamethasone on TIMP-1 production involves murine osteoblastic MC3T3-E1 cell apoptosis.
ABSTRACT High dose glucocorticoid (GC) treatment induces osteoporosis partly via increasing osteoblast apoptosis. However, the mechanism of GC-induced apoptosis has not been fully elucidated. Osteoblast-derived tissue inhibitor of metalloproteinase-1 (TIMP-1) was recently reported to be involved in bone metabolism. Our previous study demonstrated that TIMP-1 suppressed apoptosis of the mouse bone marrow stromal cell line MBA-1 (pre-osteoblast) induced by serum deprivation. Therefore, we tested the effect of the GC dexamethasone (Dex) on TIMP-1 production in murine osteoblastic MC3T3-E1 cells and further determined whether this action is associated with Dex-induced osteoblast apoptosis. Dex decreased TIMP-1 production in MC3T3-E1 cells, and this effect was blocked by the glucocorticoid receptor (GR) antagonists, RU486 and RU40555. Recombinant TIMP-1 protein reduced caspase-3 activation and apoptosis induced by Dex in MC3T3-E1 cells. In addition, the pro-apoptotic effect of the Dex was augmented by suppression of TIMP-1 with siRNA. Furthermore, mutant TIMP-1, which has no inhibitory effects on MMPs, yet protects MC3T3-E1 cells against Dex-induced apoptosis. Our study demonstrates that Dex suppresses TIMP-1 production in osteoblasts through GR, and this effect is associated with its induction of osteoblast apoptosis. The anti-apoptotic action of TIMP-1 is independent of its inhibitory effects on MMPs activities. The decrease in TIMP-1 production caused by Dex may contribute to the mechanisms of Dex-induced bone loss.
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ABSTRACT: Transplanted embryonic stem (ES) cells following myocardial infarction (MI) contribute to limited cardiac repair and regeneration with improved function. Therefore, novel strategies are still needed to understand the effects of genetically modified transplanted stem cells on cardiac remodeling. The present study evaluates whether transplanted mouse ES cells overexpressing TIMP-1, an anti-apoptotic and anti-fibrotic protein, can enhance cardiac myocyte differentiation, inhibit native cardiac myocyte apoptosis, reduce fibrosis, and improve cardiac function in the infarcted myocardium. MI was produced in C57BL/6 mice by coronary artery ligation. TIMP-1-ES cells, ES cells, or culture medium (control) were transplanted into the peri-infarct region of the heart. Immunofluorescence, TUNEL staining, caspase-3 activity, ELISAs, histology, and echocardiography were used to identify newly differentiated cardiac myocytes and assess apoptosis, fibrosis, and heart function. Two weeks post-MI, significantly (p<0.05) enhanced engraftment and cardiac myocyte differentiation was observed in TIMP-1-ES cell transplanted hearts compared with hearts transplanted with ES cells and control. Hearts transplanted with TIMP-1-ES cells demonstrated a reduction in apoptosis as well as an increase (p<0.05) in p-Akt activity compared with ES cells or culture media controls. Infarct size and interstitial and vascular fibrosis were significantly (p<0.05) decreased in the TIMP-1-ES cell group compared to controls. Furthermore, MMP-9, a key pro-fibrotic protein, was significantly (p<0.01) reduced following TIMP-1-ES cell transplantation. Echocardiography data showed fractional shortening and ejection fraction were significantly (p<0.05) improved in the TIMP-1-ES cell group compared with respective controls. Our data suggest that transplanted ES cells overexpressing TIMP-1 attenuate adverse myocardial remodeling and improve cardiac function compared with ES cells which may have therapeutic potential in regenerative medicine.Cell Transplantation 03/2012; 21(9). DOI:10.3727/096368911X627561 · 3.57 Impact Factor
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ABSTRACT: Ghrelin is a 28-amino-acid peptide that acts as a natural endogenous ligand of the growth hormone secretagogue receptor (GHSR) and strongly stimulates the release of growth hormone from the hypothalamus-pituitary axis. Previous studies have identified the important physiological effects of ghrelin on bone metabolism, such as regulating proliferation and differentiation of osteoblasts, independent of GH/IGF-1 axis. However, research on effects and mechanisms of ghrelin on osteoblasts apoptosis is still rare. In this study, we identified expression of GHSR in MC3T3-E1 cells and determined the effects of ghrelin on the apoptosis of osteoblastic MC3T3-E1 cells and the mechanism involved. Our data demonstrated that ghrelin inhibited the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation, as determined by terminal deoxynucleotidyl transferase-mediated deoxyribonucleotide triphosphate nick end-labeling (TUNEL) and ELISA assays. Moreover, ghrelin upregulated Bcl-2 expression and downregulated the Bax expressions in a dose-dependent manner. Our study also showed decreased activated caspase-3 activity under the treatment of ghrelin. Further study suggested that ghrelin stimulated the phosphorylation of ERK and AKT. Pretreatment of cells with the ERK inhibitor PD98059, PI3K inhibitor LY294002, and GHSR-siRNA blocked the ghrelin-induced activation of ERK and AKT, respectively; however, ghrelin did not stimulate the phosphorylation of p38 or JNK. PD90859, LY294002 and GHSR-siRNA attenuated the anti-apoptosis effect of ghrelin in MC3T3-E1. In conclusion, ghrelin inhibits the apoptosis of osteoblastic MC3T3-E1 cells induced by serum deprivation, which may be mediated by activating the GHSR/ERK and GHSR/PI3K/AKT signaling pathways.Toxicology and Applied Pharmacology 08/2013; DOI:10.1016/j.taap.2013.07.018 · 3.63 Impact Factor
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ABSTRACT: Glucocorticoids play a pivotal role in the proliferation of osteoblasts, but the underlying mechanism has not been successfully elucidated. In this report, we have investigated the molecular mechanism which elucidates the inhibitory effects of dexamethasone on murine osteoblastic MC3T3-E1 cells. It was found that the inhibitory effects were largely attributed to apoptosis and G1 phase arrest. Both the cell cycle arrest and apoptosis were dependent on glucocorticoid receptor (GR), as they were abolished by GR blocker RU486 pre-treatment and GR interference. G1 phase arrest and apoptosis were accompanied with a p53-dependent up-regulation of p21 and pro-apoptotic genes NOXA and PUMA. We also proved that dexamethasone can't induce apoptosis and cell cycle arrest when p53 was inhibited by p53 RNA interference. These data demonstrate that proliferation of MC3T3-E1 cell was significantly and directly inhibited by dexamethasone treatment via aberrant GR activation and subsequently P53 activation.PLoS ONE 06/2012; 7(6):e37030. DOI:10.1371/journal.pone.0037030 · 3.53 Impact Factor